Testing the Applicability of the WEPP Model for Predicting Soil Erosion and Sediment Yield in Small Philippine Watersheds

Abstract

Testing of the applicability of the state-of-the-art soil erosion prediction technology such as the USDA-ARS WEPP model in Philippine watersheds is an important initial step towards improving soil erosion estimation on a watershed scale in this erosion-prone country. This study explored the applicability of the WEPP model for predicting soil erosion and sediment yield in Philippine watersheds. The WEPP model was developed for a small watershed in southern Philippines using 22 hillslopes and using average soil, slope, management and crop cover conditions. Trial simulation run under continuous mode using breakpoint climatological data observed in a nearby weather station for year 2000 yielded erosion and sediment yield within the typical range of values for croplands and rangelands. The applicability of the WEPP model in the Philippines is constrained to a large extent by the availability of numerous input data required by the model including short increment rainfall observations, accurate and updated land cover data, agricultural management practices, spatial variability of soil properties, channel hydraulic characteristics among other input data requirements. A number of local plant species as well as local tillage practices are also currently unsupported by the current WEPP model version. Model validation is likewise constrained by the availability of accurately measured erosion rates and sediment yield. Nevertheless, initial model testing indicated a great potential in the applicability of the WEPP model on a hillslope and watershed scale for predicting soil erosion and sediment yield in tropical countries like the Philippines.